Binding a function with input argument to a tkinter widget-CodePudding

The following code which I use as an example, is a simple tkinter form with a label in it:

import tkinter

root=tkinter.Tk()
root.title('Form Title')
root.geometry('400x200 700 350')

def print_text(event, txt):
    print(txt)

lbl1=tkinter.Label(master=root, text='Click ME!', bg='green')
lbl1.bind('<Button-1>', lambda:print_text(txt='label was clicked'))
lbl1.place(x=10, y=10)

root.mainloop()

I have a function called “print_text” that is bind to the left click event of the label. This function simply accepts a string and print it out. The “event” argument is there to account for a parameter that will be passed by tkinter, and “txt” argument is the string I want to print out. Logically what I have here makes sense (at least to me), but running this code will result in the following error:
TypeError: lambda() takes 0 positional arguments but 1 was given

I would very much appreciate it, if someone explain what is the problem here and what did I do wrong.

CodePudding user response：

you need to add the event argument to your lambda, and pass it to print_text()

lbl1.bind('<Button-1>', lambda e:print_text(event=e, txt='label was clicked'))

CodePudding user response：

print_text is not the callback function; it's a function used by the callback function, which you define using a lambda expression. It's the callback itself that needs to accept the argument, not necessarily print_text.

def print_text(txt):
    print(txt) 

...

lbl1.bind('<Button-1>', lambda event: print_text(txt='label was clicked'))

Whether you use the event passed to the callback is up to you. For example, you can define print_text to accept an event, and have the callback pass it explicitly.

def print_text(event, txt):
    print("Got {event}")
    print(txt)


lbl1.bind('<Button-1>', lambda event: print_text(event, txt='label was clicked'))